Conventionally, various types of heat transfer fins have been used for, for example, home or automobile air conditioners, freezer-refrigerators, dehumidifiers, and water heaters. Fin-tube heat exchangers, in which heat transfer fins and heat transfer tubes are combined, also are commonly used. A fin-tube heat exchanger is constructed of a plurality of heat transfer fins arranged at a predetermined fin pitch, and heat transfer tubes penetrating these fins.
In this type of heat exchanger, the heat transfer coefficient of the fin increases when the velocity of the fluid flowing over the fin surface is increased. However, as the velocity of the fluid flowing over the fin surface becomes higher, the pressure loss of the fluid that passes through the heat exchanger correspondingly increases. Thus, there is a trade-off between the pressure loss and the heat transfer coefficient in the heat exchanger. In view of this, it has been desired to improve the heat transfer coefficient and at the same time prevent the pressure loss from increasing, in order to enhance the performance of the heat exchanger.
Various fin shape designs for improving the heat transfer coefficient and reducing the pressure loss have been known. For example, JP 64-90995 A discloses a corrugated fin in which a plate-shaped fin is bent in a wave-like shape. JP 7-239196 A discloses a fin-tube heat exchanger in which a large number of very small dimples are provided on the surfaces of the fins. JP 63-294494 A discloses a fin-tube heat exchanger in which projections each having a triangular pyramidal shape are provided on the surfaces of the fins. JP 6-300474 A discloses a fin-tube heat exchanger in which quadrangular pyramidal-shaped protrusions are provided on the surfaces of the fins.